In recent years, it is designed to attain miniaturization and density growth of electronic equipment, by integrating a passive part, such as a capacitor or inductor, conventionally mounted on a ceramic substrate surface into a ceramic multilayer substrate. Such a ceramic multilayer substrate is produced by forming a green sheet from a slurry of a dielectric porcelain composition and an organic solvent by doctor blade method followed by drying, printing a wiring conductor on the top surface of the sheet, forming a laminated body by laminating such green sheets of the same dielectric porcelain composition as described above, and co-firing it.
Such a ceramic multilayer substrate uses Ag or Cu with small specific resistance as the wiring conductor for performing high-performance signal processing at a high speed. Therefore, various ceramic materials have been developed for co-firing with Ag and Cu at temperatures lower than 962° C., the melting point of Ag, and 1084° C., the melting point of Cu.
In the above-mentioned ceramic multilayer substrate, a one having a dielectric constant of 10 or less is suitably used for suppressing stray capacitance or coupling capacitance between wires. While, when a capacitor is formed within the ceramic multilayer substrate, it is desirable for the ceramics constituting the capacitor to have a high dielectric constant.
The barium titanate-based dielectric porcelain composition generally has a high dielectric constant, and can form a high-capacity capacitor within the ceramic multilayer substrate. However, since it needs a sintering temperature as high as 1150 to 1200° C. or higher, Ag and Cu cannot be used as the wiring conductor to be co-fired. Therefore, it is necessary for the barium titanate-based dielectric porcelain composition to be sinterable at a temperature of 1000° C. or lower, while having practical dielectric constant and dielectric loss.
Various prior literatures are known for the barium titanate-based dielectric porcelain composition. Japanese Patent Publication No. S54-53300A describes addition of copper oxide and bismuth oxide into non-lead composition system.
Further, Japanese Patent Publication Nos. 2006-93484A and H05-325641A describe non-lead barium titanate based dielectric materials sinterable at a low temperature.
Further, according to “Japanese Journal of Applied Physics”, Vol. 45, No. 9B, 2006, pp 7360 to 7364, “Dielectric properties and Microstructures of Low-temperature-Sintered BaTiO3-Based Ceramics with CuBiO4 sintering Aid”, it is disclosed the addition of CuBi2O4 as a sintering aid to barium titanate dielectric material without the addition of a glass. It is thus confirmed that the barium titanate dielectric material can be sintered at 920° C. to provide good temperature dependence of specific dielectric constant. Specifically, it is disclosed that a specific dielectric constant of about 1900 and a dielectric loss of about 0.6 percent were obtained.
Further, many kinds of low dielectric ceramics were known in the field of ceramic multilayer substrate (Japanese Patent Publication Nos. H09-301768A, 2000-264722A and 2000-264723A).